1. Field of the Invention
This invention relates in general to injectors for dispensing fluids in fine sprays, and more particularly relates to fuel injectors for dispensing liquid fuel in fine sprays for ignition in gas turbine engines.
2. Description of the Prior Art
The art of producing sprays of liquid is extensive. Many injectors have a nozzle with a swirl chamber. One or more angled inlet slots direct the fluid to be sprayed into the swirl chamber. The inlet slots cause the fluid to create a vortex in the swirl chamber adjacent to a spray orifice. The fluid then exits through the spray orifice in a conical spray. Patents showing such injectors include U.S. Pat. Nos. 4,613,079 and 4,134,606.
It is believed it is much easier to design and manufacture relatively large nozzles for producing relatively large droplet sprays than to design and manufacture relatively small nozzles to produce relatively fine droplet sprays. This is especially true in the context of manufacturing the inlet slots, swirl chambers, and spray orifices in small nozzles.
In the combustion of fuels, for example, a nozzle that provides a spray of fine droplets improves the efficiency of combustion and reduces the production of undesirable air pollutants. In some applications, it is desirable to have very low Flow Numbers and Flow Numbers that vary from location to location. The xe2x80x9cFlow Numberxe2x80x9d relates the rate of fluid flow output to the applied inlet pressure. Flow Numbers that are less than 1.0 lb/hr.psi0.5, and even as small as 0.1 lb/hr.psi0.5, are desirable in some applications. This corresponds to swirl chambers less than 1.905 mm (0.075 inches); and exit orifices of less than 0.3048 mm (0.012 inches) diameter.
It is believed that for many years it was only possible to manufacture many of the openings and surfaces of small nozzles to create such low Flow Numbers by using relatively low volume machine tool and hand tool operations in connection with high magnification and examination techniques. This was a labor-intensive process with a high rejection or scrap rate.
One technique which has overcome this problem and produces spray nozzles having Flow Numbers as low as 0.1 lb/hr.psi0.5 is described and illustrated in U.S. Pat. No. 5,435,884. In this patent, which is owned by the assignee of the present application, a nozzle having a small swirl chamber, exit orifice and feed slots is provided that produces a fine droplet spray. The swirl chamber, exit orifice and feed slots are formed by chemical etching the surfaces of a thin metal plate. The etching produces a nozzle with very streamlined geometries thereby resulting in significant reductions in pressure losses and enhanced spray performance. The chemical etching process is easily repeatable and highly accurate, and can produce multiple nozzles on a single plate for individual or simultaneous use.
The nozzle shown and described in the ""884 patent has many advantages over the prior art, mechanically-formed nozzles, and has received acceptance in the marketplace. The nozzle has design features that allow it to be integrated into an affordable multi-point fuel injection scheme. Nevertheless, the power generation industry is faced with increasingly stringent emissions requirements for ozone precursors, such as nitrogen oxides (NOX) and carbon monoxide (CO). To achieve lower pollutant emissions, gas turbine manufacturers have adopted lean premixed (LP) combustion as a standard technique. LP combustion achieves low levels of pollutant emissions without additional hardware for steam injection or selective catalytic reduction. By premixing the fuel and air, localized regions of near stoichiometric fuel-air mixtures are avoided and a subsequent reduction in thermal NOX can be realized.
To achieve lower levels of NOX emissions, homogeneous fuel-air mixture distributions are necessary. While the nozzle shown in the ""884 patent is appropriate for many applications, it does not have an integral air swirler allowing the introduction of the fuel spray into an air flow.
While many of the known air swirlers could be used with the nozzle shown in the ""884 patent, such known air swirlers are typically produced by machining or otherwise mechanically-forming the air passages, which would substantially increase the weight and size of the nozzle in the ""884 patent. Such swirlers would also be difficult to manufacture in small detail because of the aforementioned problems associated with conventionally machining small parts.
It is therefore believed there is a demand for an injector with a nozzle that provides a spray of fine droplets of a first fluid, and includes integral, compact and lightweight structure that allows the introduction of a second fluid into or in conjunction with the first fluid. It is further believed that there is a demand, particularly for gas turbine applications, for an injector that has a nozzle with a low Flow Number and has an integral, compact and light-weight air swirler to reduce NOX and CO emissions, improve spray patternization, and provide a spray that is well dispersed for efficient combustion.
The present invention provides a novel and unique injector with a nozzle that provides a spray of fine droplets of a first fluid, and includes integral, compact and lightweight structure that allows the introduction of a second fluid into or in conjunction with the first fluid. According to one application of the invention, an injector for gas turbine applications having a nozzle with a low Flow Number is provided, together with an integral, compact and lightweight air swirler. The injector reduces NOX and CO emissions, provides good spray patternization and the spray is well dispersed for efficient combustion. In addition, the injector can be accurately and repeatably manufactured.
According to the present invention, the injector includes a plurality of thin, flat plates of etchable material disposed in adjacent, surface-to-surface contact with one another. At least one, and preferably a plurality of nozzles are formed in the plates. Each of the nozzles includes a metering set formed in one or more of the plates and providing a fine spray of a first fluid. The injector also includes an integral swirler structure formed in one or more of the plates. The swirler structure allows the introduction of a second fluid into or in conjunction with the first fluid.
The metering set preferably includes a bowl-shaped swirl chamber shaped by etching at least one of the plates. Chemical etching, electromechanical etching or other appropriate etching technique can be used to form the swirl chamber. A spray orifice, also preferably formed by etching, is in fluid communication with the center of the swirl chamber. At least one feed slot, also preferably formed by etching, is in fluid communication with the swirl chamber and extends in non-radial relation thereto. Fluid directed through the feed slot(s) moves in a vortex motion toward the-center of the swirl chamber, and then exits the spray orifice in the conical spray of fine droplets.
The swirler structure preferably provides the second fluid with a swirling component of motion. The swirler structure preferably includes a cylindrical swirler passage, also shaped by etching through at least one of the other plates. The cylindrical swirler passage is located in co-axial relation to the spray orifice of the metering set, such that the first fluid from the spray orifice passes through the swirler passage. At least one feed slot, also preferably formed by etching, is provided in fluid communication with the swirler passage and extends in non-radial relation thereto. The second fluid is provided through the feed slot and moves in a swirling motion in the swirler passage. The second fluid imparts a swirling component of motion to the first fluid as the first fluid passes through the swirler passage.
The swirler structure is preferably formed in multiple plates of the injector. Each of the plates defines a portion of the swirler passage, with the plates arranged such that the portions are in co-axial relation with one another. Each swirler passage portion can have the same diameter and dimension, or could have different diameters and/or dimensions, such as to create a conical, tapered, elliptical, or other geometry swirler passage, to further enhance the mixing of the fluids.
Each of the plates of the swirler structure further preferably includes a plurality of feed slots in fluid communication with respective swirler passage portions and extending in non-radial relation thereto for supplying multiple fluid streams to the swirler passage. The feed slots can be provided in one or more multiple plates depending upon the desired amount of the second fluid and the swirl component to be imparted to the first fluid. The feed slots can be oriented to provide fluid streams in the same direction (co-rotating), or in opposite directions (counter-rotating).
Supply passages for the second fluid extend through the plates of the metering set and the swirler structure to the feed slots in each plate of the swirler structure. Each supply passage can also feed slots of adjacent swirler passages, such that multiple nozzles can be formed in a small area to reduce the overall size of the injector.
Injectors constructed according to the present invention are lightweight and compact, and can be used to introduce a second fluid into a first fluid spray. In gas turbine applications, the injector can be used to introduce a fuel spray into a swirling air flow. The swirling air enhances mixing, thereby resulting in reductions in NOX and CO emissions from the gas turbine engine. The swirling flow also enhances flame stability by generating toroidal recirculation zones that bring combustion products back towards the fuel injection apparatus thereby resulting in a sustained combustion and a stable flame. The swirling flow also provides good spray patternization and the spray is well-dispersed for efficient combustion. The etching of the plates of the swirler structure (and of the metering set) is accurate and repeatable.
Further features of the present invention will become apparent to those skilled in the art upon reviewing the following specification and attached drawings